This invention relates generally to single lens reflex cameras, motion picture cameras and video cameras, and more particularly to an automatic focusing device in such photographing devices.
In a photographing operation, focusing and exposure are essential. Owing to the recent electronical development, the exposure can be substantially automatically determined, and accordingly the determination of exposure is not a cause that makes pictures unsatisfactory in quality.
On the other hand, a method of automatically focusing a photographing lens on an object (hereinafter referred to merely as "automatic focusing") is not sufficiently practical in use. A short focal length 35 mm camera for the beginner employing such a method has been proposed in the art. However, the camera is not ideal in that it is low in accuracy, it cannot use an interchangeable lens, and it cannot use a long focal length lens.
Recently, almost all the different types of motion picture cameras have been combined with sound systems. However, it is considerably difficult for a photographer to operate the motion picture camera while controlling both the focusing of the camera and the adjustment of the sound system. Thus, there has been a strong demand for the provision of an automatic focusing device excellent in operability.
In photographing objects with a video camera, a number of factors must be taken into account. For instance, the composition, the movement of a person or persons, and the background must be taken into consideration in operating the video camera. In addition to these factors, the arrangement of color in a natural color image is one of the factors which must be adjusted by the photographer through his experience at all times, because the monitor system of the video camera is a monochrome television receiver.
Recently, the exposure system or mechanism has been improved into an automatic one, and accordingly the photographer can operate a camera more readily. However, it is still considerably difficult for the photographer to precisely control the focusing through the small monitoring finder. Thus, also in this respect, the provision of an automatic focusing device is strongly required.
Automatic focusing devices according to a visitronic module system, an infrared ray system and an ultrasonic wave system are commercially available. Since the automatic focusing devices are not provided according to a system in which the focusing position is detected by utilizing the bundle of rays passing through the photographing optical system (hereinafter referred to as "a TTL system", when applicable), the devices are completely different from an automatic focusing device ideal for the above-described various photographing devices, being disadvantageous in the following points:
(1) The conventional automatic focusing devices are not free from parallax.
(2) Accordingly, it is impossible to display on the finder a part of the object to be photographed on which the photographing lens should be focused.
(3) It is considerably difficult to apply the conventional automatic focusing devices to a photographing device using a photographing lens such as a zoom lens having a focal length variable over a wide range; more specifically to a video camera, a motion picture camera, or a single lens reflex camera using an interchangeable lens.
(4) The conventional automatic focusing devices are low in accuracy.
In view of the foregoing, an object of this invention is to provide an ideal automatic focusing device in which all of the difficulties accompanying a conventional automatic focusing device have been eliminated by employing an automatic focusing method according to the TTL system, and which can be applied to a variety of photographing devices.
On the other hand, a variety of automatic focusing methods for a photographing device such as a motion picture camera or a video camera have been proposed in the art, in which the contrast or the like of the image of an object which is formed by the pencil of rays passing through the photographing optical system is analyzed to detect the focusing condition.
In most of the conventional automatic focusing methods, however, it is difficult to determine the focusing position with respect to the focus detecting plane, i.e. to detect the side of the focus detecting plane on which the focusing position is located.
Furthermore, in many conventional automatic focusing methods one or plural ones of the blade, grid and mirror which are arranged in a photographing system, a light receiving unit and an optical system are made movable, so that the focusing position is detected by vibrating or moving these members, so as to drive the photographing optical system to the focusing position thus detected.
However, these conventional automatic focusing methods are undesirable in that the mechanism is low in durability, the operating speed is also low, and the device itself is rather intricate.
Automatic focusing methods in which such mechanical movable members are eliminated have been proposed in the art. However, in the methods, the realization of the processing system is not taken into account yet, and accordingly it is difficult to practice the methods.
Accordingly, another object of the invention is to provide an automatic focusing device in which all of the above-described drawbacks accompanying a conventional automatic focusing device according to the TTL system have been eliminated.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.